Multi-layer coatings with an inorganic oxide network containing layer and methods for their application

ABSTRACT

Multi-layer coatings are disclosed that include (1) a first layer comprising an inorganic oxide network, and (2) a second layer applied over at least a portion of the first layer, wherein the second layer is deposited from at least one liquid composition that is hydrophilic and includes an essentially completely hydrolyzed organosilicate. Also disclosed are substrates coated with such multi-layer coatings, methods of applying such multi-layer coatings to a substrate and methods for improving the anti-fouling, self-cleaning, easy-to-clean, and/or anti-fogging properties of an article.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/575,438, filed May 28, 2004.

FIELD OF THE INVENTION

The present invention relates to multi-layer coatings that comprise afirst layer and a second layer. The coatings are hydrophilic anddurable, and may exhibit, for example, advantageous easy-to-clean,self-cleaning, anti-fouling, anti-fogging, anti-static and/oranti-bacterial properties. The coatings can, in certain embodiments, berendered super-hydrophilic upon photoexcitation of a photocatalyticmaterial.

BACKGROUND OF THE INVENTION

Hydrophilic coatings are advantageous for certain coating applications,such as where coated surfaces exhibiting anti-fouling, easy-to-clean,self-cleaning, and/or anti-fogging properties are desired. Such coatingscan be particularly useful, by way of example, for application tosurfaces exposed to the outdoor environment. Building structures as wellas other articles that are exposed to the outdoors are likely to come incontact with various contaminants, such as dirt, oil, dust, clay, amongothers. Rainfall, for example, can be laden with such contaminants. Asurface with a hydrophilic coating deposited thereon may be anti-foulingby preventing contaminants in rainwater from adhering to the surfacewhen the rainwater flows down along the coated surface. Moreover, duringfair weather air-born contaminants may come in contact with and adhereto surfaces. A surface with a hydrophilic coating deposited thereon maybe self-cleaning and/or easy-to-clean because the coating has theability to wash those contaminants away when the surface comes incontact with water, such as during a rainfall.

Coatings having self-cleaning, easy-to-clean, and/or anti-foulingproperties may also be advantageous for application to surfaces that areexposed to indoor contaminants, such as, for example, kitchencontaminants, such as oil and/or fat. An article with a hydrophiliccoating deposited thereon can be soaked in, wetted with, or rinsed bywater to release contaminants from the coating and remove them from thesurface of the article without use of a detergent.

Coatings having anti-fogging properties can be particularly useful inmany applications as well. For example, articles containing surfaceswhere visibility is important, such as windshields, windowpanes,eyeglass lenses, mirrors, and, other similar articles can benefit from acoating with anti-fogging properties because they contain surfaces thatcan often be fogged by steam or moisture condensate or blurred by waterdroplets adhering to the surface thereof. It is known that the foggingof a surface of an article results when the surface is held at atemperature lower than the dew point of the ambient atmosphere, therebycausing condensation moisture in the ambient air to occur and formmoisture condensate at the surface of the article. If the condensateparticles are sufficiently small, so that the diameter thereof is aboutone half of the wavelength of the visible light, the particles can causescattering of light, whereby the surface becomes apparently opaque,causing a loss of visibility.

A surface with a hydrophilic coating deposited thereon may beanti-fogging because such a coating can transform condensate particlesto a relatively uniform film of water, without forming discrete waterdroplets. Similarly, a surface with a hydrophilic coating depositedthereon can prevent rainfall or water splashes from forming discretewater droplets on the surface, thereby improving visibility throughwindows, mirrors, and/or eyewear.

In view of these and other advantages, various hydrophilic coatingcompositions have been proposed. Some of these coatings achieve theirhydrophilicity through the action of a photocatalytic material that isdispersed in a silicon-containing binder. For example, U.S. Pat. No.5,755,867 (“the '867 patent”) discloses a particulate photocatalystdispersed in a coat-forming element. The photocatalyst preferablyconsists of titanium dioxide particles having a mean particle size of0.1 micron or less, where the titanium dioxide may be used in either theanatase or rutile form. The coat-forming element is capable of forming acoating of silicone resin when cured and is comprised of anorganopolysiloxane formed by partial hydrolysis of hydrolyzable silanesfollowed by polycondensation. In the '867 patent, the siliconecoat-forming element in itself is considerably hydrophobic, but uponexcitation of the dispersed photocatalyst, a high degree of wateraffinity, i.e., hydrophilicity, can be imparted to the coating.

Japanese Patent Application JP-8-164334A discloses a coatingfilm-forming composition comprising titanium oxide having an averageparticle diameter of 1 to 500 nanometers, a hydrolyzate of ahydrolyzable silicon compound, and a solvent. The hydrolyzable siliconcompound is an alkyl silicate condensate expressed by the formulaSi_(n)O_(n-1)(OR)_(2n+2) (where n is 2 to 6, and R is a C1-C4 alkylgroup). The hydrolyzate results from hydrolyzing the alkyl silicatecondensate at a hydrolysis percentage of 50 to 1500%. The hydrolyzateitself, however, is not believed to be hydrophilic.

U.S. Pat. Nos. 6,013,372 and 6,090,489 disclose photocatalytic coatingcompositions wherein particles of photocatalyst are dispersed in afilm-forming element of uncured or partially cured silicone(organopolysiloxane) or a precursor thereof. The photocatalyst mayinclude particles of a metal oxide, such as the anatase and rutile formsof titanium dioxide. According to these patents, the coatingcompositions ate applied on the surface of a substrate and thefilm-forming element is then subjected to curing. Then, uponphotoexcitation of the photocatalyst, the organic groups bonded to thesilicon atoms of the silicone molecules of the film-forming element aresubstituted with hydroxyl groups under the photocatalytic action of thephotocatalyst. The surface of the photocatalytic coating is thereby“superhydrophilified,” i.e., the surface is rendered highly hydrophilicto the degree that the contact angle with water becomes less than about100. In these patents, however, the film-forming element in itself isconsiderably hydrophobic, i.e., the initial contact angle with water isgreater than 50°. As a result, the coating is initially hydrophobic, andit is only upon excitation of the dispersed photocatalyst thathydrophilicity is imparted to the coating.

U.S. Pat. No. 6,165,256 discloses compositions that can hydrophilify thesurface of a member to impart anti-fogging properties to the surface ofthe member. The compositions disclosed in this patent comprise (a)photocatalytic particles of a metallic oxide, (b) a precursor capable offorming a silicone resin film or a precursor capable of forming a silicafilm, and (c) a solvent, such as water, organic solvents, and mixturesthereof. The solvent is added in an amount such that the total contentof the photocatalytic particle and the solid matter of the precursor inthe composition is 0.01 to 5% by weight. As in the previous examples,however, hydrophilification of the coating formed from such acomposition takes place upon photoexcitation of the photocatalyst, whilethe film forming material in itself is not hydrophilic. Therefore, thecoating is not believed to be hydrophilic prior to excitation of thephotocatalyst.

The prior art hydrophilic coatings that achieve their hydrophilicitythrough the action of a photocatalytic material that is dispersed in asilicon-containing binder suffer, however, from some drawbacks. Onenotable drawback is that these coatings do not exhibit hydrophilicityuntil photoexcitation of the photocatalyst. In addition, thesecompositions typically require a forced cure, i.e., they cannot beefficiently cured at room temperatures.

U.S. Pat. No. 6,303,229 (“the '229 patent”) discloses anothercomposition that may include a photocatalytic material. The coatingdisclosed in the '229 patent is formed from applying a coatingcomposition that contains a silicone resin, which acts as the binder andwhich is obtained by hydrolyzing and condensation-polymerizing certaintetra-functional alkoxysilanes. The coating compositions may alsoinclude colloidal silica. Evidently, the coated film formed from thecomposition disclosed in the '229 patent can be initially hydrophilic.This initial hydrophilicity, however, is believed to result from thepresence of colloidal silica in the composition rather than the siliconeresin itself. It is believed that the silicone resin disclosed in the'229 patent is not itself hydrophilic because the desired pH of theresin is 3.8 to 6.0, which indicates that Si—OR groups exist in theresin in an amount to prevent gellation and hydrophilicity.

It would be advantageous to provide multi-layer coatings that include acoating layer comprising an inorganic oxide network and a coating layerdeposited from a liquid composition that is hydrophilic and comprises anessentially completely hydrolyzed organosilicate.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart reflecting a Fourier Transform Infrared. Spectroscopy(“FTIR”) analysis of a dry film formed from a binder material used inaccordance with certain non-limiting embodiments of the presentinvention;

FIG. 2 is a schematic cross-sectional view in an enlarged scale ofcertain non-limiting embodiments of the second layer of the multi-layercoatings of the present invention; and

FIG. 3 is a Field Emission Scanning Electron Microscope SecondaryElectron Micrograph (magnification 40,000×) depicting certainnon-limiting embodiments of the second layer of the multi-layer coatingsof the present invention.

FIG. 4 is a chart illustrating the results of the durability testingconducted as described in Example 2.

SUMMARY OF THE INVENTION

In one respect, the present invention is directed to multi-layercoatings comprising (1) a first layer comprising an inorganic oxidenetwork, and (2) a second layer applied over at least a portion of thefirst layer, wherein the second layer is deposited from at least oneliquid composition that is hydrophilic and comprises an essentiallycompletely hydrolyzed organosilicate.

In another respect, the present invention is directed multi-layercoatings comprising (1) a first layer comprising an inorganic oxidenetwork, and (2) a second layer applied over at least a portion of thefirst layer, wherein the second layer is deposited from at least oneliquid composition that comprises (a) a photocatalytic material, and (b)a binder that is hydrophilic and comprises an essentially completelyhydrolyzed organosilicate.

In still another respect, the present invention is directed tosubstrates coated with a multi-layer coating of the present invention.

In yet another respect, the present invention is directed to methods ofapplying a multi-layer coating to a substrate comprising the steps of(1) applying to a substrate a first layer comprising an inorganic oxidenetwork; (2): applying onto at least a portion of the first layer aliquid composition from which a second layer is deposited, wherein thecomposition of the second layer is, hydrophilic and comprises anessentially completely hydrolyzed organosilicate; and (3) curing thesecond layer.

The present invention is also directed to methods of applying amulti-layer coating to a substrate comprising the steps of (1) applyingto a substrate a first layer comprising an inorganic oxide network; (2)applying onto at least a portion of the first layer a liquid compositionfrom which a second layer is deposited over the first layer, wherein theliquid composition of the second layer comprises (a) a photocatalyticmaterial, and (b) a binder that is hydrophilic and comprises anessentially completely hydrolyzed organosilicate; and (3) curing thesecond layer.

The present invention is also directed to methods for improving theanti-fouling, self-cleaning, easy-to-clean, and/or anti-foggingproperties of an article, wherein the article comprises a surface havinga coating comprising a inorganic oxide network deposited thereon, themethod comprising: (1) applying to at least a portion of the surface aliquid composition comprising an essentially completely hydrolyzedorganosilicate; and (2) curing the liquid composition applied in step(1).

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

For purposes of the following detailed description, it is to beunderstood that the invention may assume various alternative variationsand step sequences, except where expressly specified to the contrary.Moreover, other than in any operating examples, or where otherwiseindicated, all numbers expressing, for example, quantities ofingredients used in the specification and claims are to be understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

In this application, the use of the singular includes the plural andplural encompasses singular, unless specifically stated otherwise. Forexample, and without limitation, this application refers to liquidcompositions that comprise “a photocatalytic material”. Such referencesto “a photocatalytic material” is meant to encompass compositionscomprising one photocatalytic material as well as compositions thatcomprise more than one photocatalytic material, such as compositionsthat comprise two different photocatalytic materials. In addition, inthis application, the use of “or” means “and/or” unless specificallystated otherwise, even though “and/or” may be explicitly used in certaininstances.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

In one respect, the present invention is directed to multi-layercoatings comprising (1) a first layer comprising an inorganic oxidenetwork, and (2) a second layer applied over at least a portion of thefirst layer, wherein the second layer is deposited from at least oneliquid composition that is hydrophilic and comprises an essentiallycompletely hydrolyzed organosilicate.

The multi-layer coatings of the present invention comprise a first:layer that comprises an inorganic oxide network. As used herein, theterm “network” refers to an interconnected chain or group of molecules.

In certain embodiments, the first layer of the multi-layer coatings ofthe present invention is deposited from a composition comprising a solcontaining a network-forming metal alkoxide, such as an alkoxysilaneand/or an alkoxide of another metal, such as zirconium, titanium andaluminum. The alkoxysilane, if used, may be an organoalkoxysilane, suchas an alkylalkoxysilane or organofunctional alkoxysilane. The alkoxidemay contain alkyl or aryl groups and may be in dimer or higher condensedform so long as hydrolysable alkoxide groups remain.

In certain embodiments, the network-forming metal alkoxide is analkoxysilane of the general formula R_(x)Si(OR′)_(4-x) wherein R is anorganic radical, R′ is selected from the group consisting of lowmolecular weight alkyl radicals, such as methyl, ethyl, propyl, andbutyl radicals, and x is an integer and is at least one and is less than4. The organic radical of R may, for example, be alkyl, vinyl,methoxyethyl, phenyl, y-glycidoxypropyl, or y-methacryloxypropyl, amongothers, including mixtures thereof. The alkoxide hydrolyzes according tothe general reaction set forth below, where R, R′ and x are as describedabove and y is less than 4.R_(x)Si(OR′)_(4-x)+yH₂O→R_(x)Si(OR′)_(4-x-y)(OH)_(y)+yR—OHCondensation of the hydrolyzed alkoxide proceeds according to thegeneral reactions

Further hydrolysis and condensation follow.

In certain embodiments, the first layer of the multi-layer coatings ofthe present invention may comprise other components, such as ultravioletradiation absorbers, organic film-forming polymers, and components toimprove flow properties, abrasion resistance and/or durability.Non-limiting examples of compositions from which the first layer of themulti-layer, coatings of the present invention may be formed, andmethods for their production, are described in U.S. Pat. Nos. 4,753,827,4,754,012, 4,799,963, 5,035,745, 5,199,979, 6,042,737 and 6,106,605,which are incorporated herein by reference.

In certain embodiments, the first layer of the multi-layer coatings ofthe present invention is transparent. As used herein, the term“transparent” is intended to mean that the cured coating does notsubstantially change the percentage of visible light transmitted througha transparent polymeric substrate to which it may be applied. Thetintability of a coating is a function of the amount of dye that thecoating acquires under certain defined conditions which is expressedquantitatively by the percentage of light transmitted through the dyedcoating. The tintability of a coating can be measured as described inU.S. Pat. No. 6,042,737 at col. 4, line 57 to col. 5, line 8, which isincorporated herein by reference.

Examples of commercially available compositions that are suitable foruse in depositing the first layer of the multi-layer coatings of thepresent invention, are the Hi-Gard™ and SolGard® coating solutionsavailable from PPG Industries, Inc., the Crizol® products available fromEssilor International, S.A. and the CrystalCoat™ products available fromSDC Technologies, Inc., among others.

The multi-layer coatings of the present invention comprise a secondlayer applied over at least a portion of the first layer, wherein thesecond layer is deposited from at least one liquid: composition thatcomprises an essentially completely hydrolyzed organosilicate. As usedherein, the term “organosilicate” refers to a compound containingorganic groups bonded to a silicon atom through an oxygen atom. Suitableorganosilicates include, without limitation, organoxysilanes containingfour organic groups bonded to a silicon atom through an oxygen atom andorganoxysiloxanes having a siloxane main chain ((Si—O)_(n)) constitutedby silicon atoms.

The organic groups bonded to the silicon atom through an oxygen atom inthe organosilicates are not limited and may include, for example,linear, branched or cyclicalkyl groups. Specific examples of the organicgroups that may be bonded to the silicon atom through an oxygen atom inthe organosilicates include, without limitation, methyl, ethyl,n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, i-pentyl,neopentyl, hexyl, octyl or the like. Of these alkyl groups, C₁ to C₄alkyl groups are often used. Examples of other suitable organic groupsmay include aryl, xylyl, naphthyl or the like. The organosilicate maycontain two or more different kinds of organic groups.

Specific non-limiting examples of suitable organoxysilanes aretetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane,tetraisopropoxysilane, tetra-n-butoxysilane, tetraisobutoxysilane,tetra-sec-, butoxysilane, tetra-t-butoxysilane, tetraphenoxysilane, anddimethoxydiethoxysilene. These organosilicates may be used alone or incombination of any two or more thereof. Among these organosilicates,tetramethoxysilane and/or partially hydrolyzed condensates thereof showa high reactivity for hydrolysis and, therefore, can readily producesilanol groups.

Specific non-limiting examples of suitable organoxysiloxanes arecondensates of the above organoxysilanes. The condensation degree of theoganoxysiloxanes is not particularly restricted. In certain embodiments,the condensation degree lies within the range represented by thefollowing formula:SiO_(x)(OR)_(y)wherein x is 0 to 1.2, and y is: 1.4 to 4 with the proviso that (2x+y)is 4; and R is an organic group, such as C₁ to C₄ alkyl.

The factor or subscript x represents the condensation degree of thesiloxane. When the siloxane shows; a molecular weight distribution, thefactor x means an average condensation degree. Compounds represented bythe above formula wherein x=0, are organoxysilanes as a monomer, andcompounds represented by the above formula wherein 0<x<2, are oligomerscorresponding to condensates obtained by partial hydrolysiscondensation. Also, compounds represented by the above formula whereinx=2, corresponds to SiO₂ (silica). In certain embodiments, thecondensation degree x of the organosilicate used in the presentinvention is in the range of 0 to 1.2, such as 0 to 1.0. The siloxanemain chain may have a linear, branched or cyclic structure or a mixturethereof. The above formula: SiO_(x)(OR)_(y) may be determined by Si—NMRas described in U.S. Pat. No. 6,599,976 at col. 5, lines 10 to 41,incorporated herein by reference.

As mentioned earlier, the organosilicate of the liquid composition fromwhich the second layer is deposited is essentially completelyhydrolyzed. As used herein, the term “essentially completely hydrolyzedorganosilicate” refers to a material wherein the organoxy groups of theorganosilicate are substantially replaced by silanol groups to an extentthat the material is rendered hydrophilic. As used herein, the term“hydrophilic” means that the material has an affinity for water. One wayto assess the hydrophilicity of a material is to measure the contactangle of water with a dry film formed from the material: In certainembodiments of the present invention, the composition from which thesecond layer is deposited comprises a hydrolyzed organosilicate that canform a dry film exhibits a water contact angle of no more than 20°, or,in other embodiments, no more than 15°, or, in yet other embodiments, nomore than 10°. This hydrolysis may produce a network polymer, asillustrated below:

where m and n are positive numbers and m is no more than n. In certainembodiments of the present invention, the essentially completelyhydrolyzed organosilicate is substantially free of —OR groups asdetermined by FTIR or other suitable analytical technique.

As a result, in certain embodiments of the present invention, themulti-layer coating exhibits an initial water contact angle of no morethan 20° or, in some embodiments, no more than 15°, or, in yet otherembodiments, no more than 10°, prior to photoexcitation of anyphotocatalytic material that may be present in the liquid compositionfrom which the second layer is deposited, as described below. The watercontact angles reported herein are a measure of the angle between atangent to the drop shape at the contact point and the surface of thesubstrate as measured through the drop and may be measured by thesessile drop method using a modified captive bubbleindicator:manufactured by Lord Manufacturing, Inc., equipped withGaertner Scientific goniometer optics. The surface to be measured isplaced in a horizontal position, facing upward, in front of a lightsource. A sessile drop of water is placed on top of the surface in frontof the light source so that the profile of the sessile drop can beviewed and the contact angle measured in degrees through the goniometertelescope which is equipped with circular protractor graduations.

Referring now to FIG. 1, there is seen a chart reflecting an FTIRanalysis of a dry film formed from such a hydrophilic material. As isapparent, significant peaks are observed at the Si—OH bond wavenumber,which is 920-950, and the Si—O—Si bond wavenumber, which is 1050-1100.On the other hand, it is apparent that the film is substantially free of—OR groups, where R represents C₁ to C₄ alkyl groups, as evidenced bythe absence of any substantial peak at the Si—OR wavenumber, which is2900-3000.

In certain embodiments, the essentially completely hydrolyzedorganosilicate included in the composition from which the second layerof the multi-layer coating of the present invention is deposited is theproduct of the hydrolysis of an organosilicate with a large amount ofwater in the presence of an acid hydrolysis catalyst. The hydrolysis maybe conducted with water present in an amount considerably greater thanthe stoichiometric amount capable of hydrolyzing organoxy groups of theorganosilicate. It is believed that the addition of such an excessiveamount of water allows silanol groups produced by hydrolysis of theorganosilicate to coexist with a large amount of water, therebypreventing the condensation reaction of the silanol groups.

The hydrolysis of the organosilicate may be conducted in the presence ofone or more acid hydrolysis catalysts. Specific examples of suitablecatalysts include, without limitation, inorganic acids, such ashydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, amongothers; organic acids, such as acetic acid, benzenesulfonic acid,toluenesulfonic acid, xylenesulfonic acid, ethylbenzenesulfonic acid,benzoic acid, phthalic acid, maleic acid, formic acid, citric acid, andoxalic acid, among others; alkali catalysts, such as sodium hydroxide,potassium hydroxide, calcium hydroxide, ammonia; and organic aminecompounds, organometallic compounds or metal alkoxide compounds otherthan the organosilicates, e.g., organotin compounds, such as dibutyl tindilaurate, dibutyl tin dioctdate and dibutyl tin diacetate,organoaluminum: compounds, such as aluminum tris(acetylacetonate),aluminum monoacetylacetonate bis(ethylacetoacetate), aluminumtris(ethylacetoacetate) and ethylacetoacetate aluminum diisopropionate,organotitanium compounds, such as titanium tetrakis(acetylacetonate),titanium bis(butoxy)-bis(acetylacetonate) and titanium tetra-n-butoxide,and organozirconium compounds, such as zirconiumtetrakis(acetylacetonate), zirconium bis(butoxy)-bis(acetylacetonate),zirconium (isopropoxy)-bis(acetylacetonate)and zirconiumtetra-n-butoxide, and boron compounds, such as boron tri-n-butoxide andboric acid; or the like.

In certain embodiments, the liquid composition from which the secondlayer of the multi-layer coatings of the present invention is depositedmay also comprise, in addition to water, an organic solvent, such asalcohols, glycol derivatives, hydrocarbons, esters, ketones, ethers orthe like. These solvents may be used alone or in the form of a mixtureof any two or more thereof.

Specific examples of alcohols that may be used include, withoutlimitation, methanol, ethanol, n-propanol, isopropanol, n-butanol,isobutanol, acetylacetone alcohol or the like. Specific examples ofglycol derivatives that may be used include, without limitation,ethylene glycol, ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, propylene glycol, propylene glycol monomethyl ether,propylene glycol monoethyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, ethylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, propylene glycolmonomethyl ether acetate, propylene glycol monoethyl ether acetate orthe like. Specific examples of hydrocarbons that may be used include,without limitation, benzene, toluene, xylene, kerosene, n-hexane or thelike. Specific examples of esters that may be used include, withoutlimitation, methyl acetate, ethyl acetate, propyl acetate, butylacetate, methyl acetoacetate, ethyl acetoacetate, butyl acetoacetate orthe like. Specific examples of the ketones that may be used includeacetone, methyl ethyl ketone, methyl isobutyl ketone, acetyl acetone orthe like. Specific examples of ethers that may be used include, withoutlimitation, ethyl ether butyl ether, methoxy ethanol, ethoxy ethanol,dioxane, furan, tetrahydrofuran or the like.

Materials suitable for use in the liquid compositions from which thesecond layer of the multi-layer coatings of the present invention isdeposited and methods for their production are described in U.S. Pat.No. 6,599,976 at col. 3, line 57. to col. 10, line 58, incorporatedherein by reference. Non-limiting examples of commercially availablematerials that are essentially completely hydrolyzed organosilicates,and which are suitable for use in the compositions from which the secondlayer of the multi-layer coatings of the present invention is deposited,are MSH-200, MSH-400, and MSH 500 silicates, available from MitsubishiChemical Corporation, Tokyo, Japan, and Shinsui Flow MS-1200 silicate,available from Dainippon Shikizai, Tokyo, Japan.

In certain embodiments, the binder is prepared in a multi-stage processwherein, in a first stage, an organoxysilane, such as any of thosementioned earlier, is reacted with water in the presence of an acidhydrolysis catalyst, such as any of those mentioned earlier, wherein thewater is present in an amount that is less than the stoichiometricamount capable of hydrolyzing the organoxy groups of the organoxysilane.In certain embodiments, the acid hydrolysis catalyst comprises anorganic acid. In certain embodiments, the water is present during thefirst stage in a stoichiometric amount capable of hydrolyzing 50 percentof the organoxy groups of the organoxysilane. The result of the firststage is a partial hydrolysis polycondensation reaction product.

In certain embodiments, the first stage of the multi-stage binderpreparation process is conducted at conditions that limit the degree ofcondensation of Si—OH groups formed as a result of the hydrolysisreaction. Such conditions can include, for example, controlling thereaction exotherm by, for example, external cooling, controlling therate of addition of the acid catalyst, and/or conducting the first stagehydrolysis in the substantial absence (or complete absence) of anyorganic cosolvent.

In a second stage, the partial hydrolysis polycondensation reactionproduct is then contacted with a large amount of water, often in theabsence of an acid hydrolysis catalyst. The amount of water used in thesecond stage is considerably greater (by “considerably greater” it ismeant that the resulting solution contains no more than 2% solids) thanthe stoichiometric amount capable of hydrolyzing organoxy groups of theorganoxysilane.

In yet other embodiments, the binder is prepared by starting with atetraalkoxysilane oligomer, such as those commercially available fromMitsubishi. Chemical Corp under the tradenames MKC Silicate MS-51, MKCSilicate MS-56 and MKC Silicate, MS-60 (all trademarks; products ofMitsubishi Chemical Corp.). Such an oligomer is reacted with water inthe presence of an organic acid hydrolysis catalyst (such as, forexample, acetic acid) and/or an organic solvent, wherein the water ispresent in an amount that is considerably greater than thestoichiometric amount capable of hydrolyzing organoxy groups of thetetralkoxysilane.

In certain embodiments, the amount of organosilicate that is present inthe liquid composition from which the second layer of the multi-layercoating is deposited ranges from 0.1 to 2 percent by weight calculatedas SiO₂ in the organosilicate, such as 0.2 to 0.90 percent by weightbased on the total weight of the composition. In these embodiments, theamount of the organosilicate that may be present in the liquidcomposition from which the second layer is deposited can range betweenany combination of the recited values, inclusive of the recited values.It will be understood by those skilled in the art that the amount of theorganosilicate present in the liquid composition from which the secondlayer of the multi-layer coating is deposited is determined by theproperties desired to be incorporated into the composition.

In certain embodiments, the multi-layer coatings of the presentinvention comprise a second layer applied over at least a portion of thefirst layer, wherein the second layer is deposited from at least oneliquid composition comprising a (a) a photocatalytic material, and (b) abinder. In these embodiments, the binder is hydrophilic and comprises anessentially completely hydrolyzed organosilicate, such as thosediscussed above. As used herein, the term “binder” refers to acontinuous material in which particles of the photocatalytic materialare dispersed.

In these embodiments, the second layer is deposited from a liquidcomposition that comprises a photocatalytic material in addition to thehydrophilic binder. As used herein, the term “photocatalytic material”refers to a material that is photoexcitable upon exposure to, andabsorption of, radiation, such as ultraviolet or visible radiation. Aphotocatalytic material is a material that, when exposed to light havinghigher energy than the energy gap between the conduction band and thevalence band of the crystal, causes excitation of electrons in thevalence band to produce a conduction electron and leaving a hole behindon the particular valence band. In certain embodiments, thephotocatalytic material comprises a metal oxide, such as zinc oxide, tinoxide, ferric oxide, dibismuth trioxide, tungsten trioxide, strontiumtitanate, titanium dioxide, or mixtures thereof.

In certain embodiments, at least a portion of the photocatalyticmaterial is present in the liquid composition from which the secondlayer is deposited in the form of particles having an averagecrystalline diameter of 1 to 100 nanometers, such as 3 to 35 nanometers,or, in yet other embodiments, 7 to 20 nanometers. In these embodiments,the average crystalline diameter of the particles can range between anycombination of the recited values, inclusive of the recited values. Itwill be understood by those skilled in the art that the averagecrystalline diameter of the particles may be selected based upon theproperties desired to be incorporated into the second layer. In someembodiments, substantially all of the photocatalytic material is presentin the composition from which the second layer is deposited in the formof such particles. The average crystalline diameter of thephotocatalytic metallic oxide particles may be determined by scanningelectron microscope or transmission electro-microscope and the crystalphase of such particles may be determined by X-ray diffraction, as knownby those skilled in the art.

As mentioned above, certain materials may be photocatalytic uponexposure to, and absorption of, for example, ultraviolet (“UV”), and/orvisible radiation. In certain embodiments, the photocatalytic materialsthat are present comprise materials that are photoexcitable by one ormore of these mechanisms. Examples of materials that may be used as partof the liquid composition from which the second layer of the multi-layercoatings of the present invention is deposited, and which arephotocatalytic upon exposure to UV radiation include, withoutlimitation, tin oxide, zinc oxide, and the brookite, anatase and rutileforms of titanium dioxide. Examples of materials that may be used aspart of the liquid composition from which the second layer of themulti-layer coatings of the present invention are deposited, and whichare photocatalytic upon exposure to visible radiation include, withoutlimitation, the brookite form of titanium oxide, titanium dioxidechemically modified via flame pyrolysis of titanium metal, nitrogendoped titanium dioxide, and plasma treated titanium dioxide.

In certain embodiments, the photocatalytic material is provided in theform of a sol comprising particles of photocatalytic material dispersedin water, such as a titania sol. Such sols are readily available in themarketplace. Examples of such materials, which are suitable for use aspart of the liquid composition from which the second layer of themulti-layer coatings of the present invention is deposited, include,without limitation, S5-300A and S5-33B available from MilleniumChemicals, STS-01, STS-02, and STS-21 available from Ishihara SangyoCorporation, and NTB-1, NTB-13 and NTB-200 available from Showa DenkoCorporation.

In certain embodiments, the photocatalytic material is present in theform of a sol comprising brookite-type titanium oxide particles or amixture of brookite-type with anatase-type and/or rutile-type titaniumoxide particles dispersed in water. Such sols can be prepared byhydrolysis of titanium tetrachloride under certain conditions, such asis taught by U.S. Pat. No. 6,479,031, which is incorporated herein byreference. Sols of this type which are suitable for use in the presentinvention include, without limitation. NTB-1 and NTB-1 3 titania solsavailable from Showa Denko Corporation.

In certain embodiments, the photocatalytic material comprises chemicallymodified titanium dioxide. Examples of such materials include titaniumdioxide chemically modified by flame pyrolysis as described by Khan etal., Efficient Photochemical Water Splitting by a Chemically Modifiedn-TiO ₂, Science Reprint, Volume 297, pp. 2243-2245 (2002), which isincorporated herein by reference, nitrogen-doped titaniumoxide:manufactured as described in U.S. Patent Application Publication2002/0169076A1l at, for example, paragraphs [0152] to [0203], which isincorporated herein by reference and/or plasma treated titanium dioxideas described in U.S. Pat. No. 6,306,343 at col. 2, line 49 to col. 7,line 17, which is incorporated herein by reference.

In certain embodiments, the amount of the photocatalytic material thatis present in the liquid composition from which the second layer of themulti-layer coating is deposited ranges from 0.05 to 5 percent solids byweight, such as 0.1 to 0.75 percent solids by weight, with percentsolids by weight being based on the total solution weight of thecomposition. In these embodiments, the amount of photocatalytic materialthat may be present can range between any combination of the recitedvalues, inclusive of the recited values. It will be understood by thoseskilled in the art that the amount of photocatalytic material present inthe liquid composition from which the second layer of the multi-layercoating is deposited is determined by the properties desired to beincorporated into that layer.

In certain embodiments, the photocatalytic material and the essentiallycompletely hydrolyzed organosilicate are present in the liquidcomposition from which the second layer is deposited at a ratio of0.05:0.95 to 5:0.3 by weight, or, in other embodiments 0.10:0.90 to3.0:0.5 by weight, or, in yet other embodiments, 0.2:0.6 by weight. Inthese embodiments, the ratio of the photocatalytic material to theorganosilicate can range between any combination of the recited values,inclusive of the recited values. It will be understood by those skilledin the art that the ratio of photocatalytic material and organosilicatein the composition of the second layer is determined by the propertiesdesired to be incorporated into that layer, such as the refractive indexdesired for the composition which may be determined with reference tothe substrate upon which the composition is to be applied.

In certain embodiments, the liquid composition from which the secondlayer of the multi-layer coating of the present invention is depositedcomprises a binder that exhibits anti-static properties, i.e., thebinder can form a dry film that has the ability to dissipateelectrostatic charges. As will be appreciated by those skilled in theart, one way to assess the anti-static capability of a material is tomeasure the surface resistivity of the material. In certain embodiments,the binder of the composition of the second layer comprises a materialthat can form a dry film that exhibits a surface resistivity of from7.5×10⁹ to 1.5×10¹² ohms/cm², or, in other embodiments, no more than10×10¹⁰ ohms/cm². The surface resistivities reported herein can bedetermined with an ACL Statitide Model 800 Megohmeter using either (1)large extension probes placed 5 millimeters apart at several locationson the sample, or (2) the meter's onboard probes spaced 2¾ inches apartat several locations on the sample. As a result, the present inventionis also directed to multi-layer coating having a second layer havingsuch anti-static properties.

In certain embodiments, the liquid composition from which the secondlayer of the multi-layer coatings of the present invention is depositedcan further include inorganic particles, for example, silica, alumina,including treated alumina (e.g. silica-treated alumina known as alphaaluminum oxide), silicon carbide, diamond dust, cubic boron nitride, andboron carbide. Such inorganic particles may, for example, besubstantially colorless, such as silica, for example, colloidal silica.Such materials may provide enhanced mar and scratch resistance. Suchparticles can have an average particle size ranging from sub-micron size(e.g. nanosized particles) up to 10 microns depending upon the end useapplication of the composition and the desired effect.

In certain embodiments, such particles comprise inorganic particles thathave an average particle, size ranging from 1to 10 microns, or from 1 to5 microns prior to incorporation into the liquid composition. In otherembodiments, the particles may have an average particle size rangingfrom 1 to less than 1000 nanometers, such as 1 to 100 nanometers, or, incertain embodiments, 5 to 50 nanometers, prior to incorporation into theliquid composition. In some embodiments, inorganic particles have anaverage particle size ranging from 5 to 50, or 5 to 25 nanometers priorto incorporation into the liquid composition. The particle size mayrange between any combination of these values inclusive of the recitedvalues.

In certain embodiments, the particles can be present in the liquidcomposition from which the second layer of the multi-layer coating isdeposited in an amount ranging from:up to 5.0 percent by weight, or from0.1 to 1.0 weight percent; or from 0.1 to 0.5 weight percent based ontotal weight of the composition. The amount of particles present in theliquid composition can range between any combination of these valuesinclusive of the recited values.

In certain embodiments, the liquid composition from which the secondlayer of the multi-layer coating is deposited also comprises anantimicrobial enhancing material, such as, for example, metals; such assilver, copper, gold, zinc, a compound thereof, or a mixture thereof;quaternary ammonium compounds, such as benzalkonium chlorides,dialkyldimethyl-ammonium chlorides, cetyltrimethyl-ammonium bromide,cetylpyridinium chloride, and3-(trimethoxysilyl)-propyldimethyl-octadecyl-ammonium chloride;phenolics, such as 2-benzyl4-chlorophenol, o-phenylphenol, sodiumo-phenylphenate, pentachlorophenol,2(2′,4′-dichlorophenoxy)-5-chlorophenol, and 4-chloro-3-methylphenol;halogen compounds, such as trichloroisocyanurate, sodiumdichloroisocyanurte, potassium dichloroisocyanuratemonotrichloroisocyanurate, potassium dichloro-isocyanurate, 1:4dichlorodimethylhydantoin, bromochlorodimethylhydantoin,2,2′-dibromo-3-nitrilopropionamide, bis(1,4-bromoacetoxy)-2-butene,1,2-dibromo-2,4-dicyarobutane, 2-bromo-2-nitropropane-1,3-diol, andbenzyl bromoacetate; organometallics, such as10,10′-bxybisphenoxi-arsine, tributyltin oxide, tributyltin fluoride,copper 8-quinolinolate, copper naphthenate, chromated copper arsenate,ammoniacal copper arsenate, and cuprous oxide; organosulfur compounds,such as methylenebisthiocyanate (MBT), vinylenebisthiocyanate,chloroethylenebisthiio-cyanate, sodium dimethyldithiocarbamate, disodiumethylenebisdithiocarbamate, zinc dimethyldithiocarbamate, andbis(trichloromethyl) sulfone; heterocyclics, such astetrahydro-3,5-dimethyl-2H-1,3,5-thiadiazine-2-thione (DMTT), sodiumpyridinethione, zinc pyridinethione, 1,2-benzisothiazoline-3-one,2-(n-octyl)-4-isothiazolin-3-one, 2-(4-thiazolyl)benzimidazole,N-(trichloromethylthio)-4-cyclohexene-1,2-dicarboximide,N-(trichloromethylthio)-phthalimide, and5-chloro-2-methyl-4-isothiazolin-3-one 2-methyl-4-isothiazolin-3-one;and nitrogen compounds, such as N-cocotrimethylenediamine,N-[α-(1-nitroethyl)benzyl]-ethylenediamine,2-(hydroxymethyl)amino-ethanol, 2-(hydroxymethyl)amino-2-methylpropanol,2-hydroxymethyl-2-nitro-1,3-propanediol,hexahydro-1,3,5-tris-(2-hydroxyethyl)-s-triazine,hexahydro-1,3,5-triethyl-s-triazine, 4-(2-nitrobutyl)morpholine+4,4′-(2-ethyl-2-nitro-trimethylene)-dimorpholine, glutaraldehyde,1,3-dimethylol-5,5-dimethyl-hydantoin, and imidazolidinyl urea, andmixtures thereof.

The liquid composition from which the second layer is deposited may, incertain embodiments, include a quantity of antimicrobial agentsufficient to exhibit an efficacy against microbes and particularlyvarious species of fungi. More specifically, in certain embodiments, thesecond layer of the multi-layer coatings of the present invention may bedeposited from a liquid composition that contains a quantity ofantimicrobial agent sufficient to inhibit microbial growth on asubstrate tested in accordance with MTCC (American Association ofChemists & Colorists) Test Method 30, Part III. Those skilled in the artare familiar with this test method and its parameters. In certainembodiments, the amount of antimicrobial enhancing material that ispresent in the liquid composition from which the second layer isdeposited ranges from 0.01 to 1.0 percent by weight, such as 0.1 to 1.0percent by weight, or, in other embodiments, 0.1 to 0.5 percent byweight based on the total weight of the composition. In theseembodiments, the amount of the antimicrobial enhancing material that maybe present in the liquid composition can range between any combinationof the recited values, inclusive of the recited values.

In certain embodiments, the liquid composition from which the secondlayer of the multi-layer coatings of the present invention is depositedmay comprise an optical activity enhancer, such as platinum, gold,palladium, iron, nickel, or, soluble salts thereof. The addition ofthese materials to compositions comprising a photocatalytic material isknown to enhance the redox activity of the photocatalyst, promotingdecomposition of contaminants adhering to the coating surface. Incertain embodiments, the amount of optical activity enhancer present inthe liquid composition from which the second layer of the multi-layercoating is deposited ranges from 0.01 to 1.0 percent by weight, such as0.1 to 1.0 percent by weight, or, in other embodiments, 0.1 to 0.5percent by weight based on the total weight of the compositions. Inthese embodiments, the amount of optical activity enhancer that may bepresent can range between any combination of the recited values,inclusive of the recited values. In certain embodiments, the liquidcomposition from which the second layer of the multi-layer coatings ofthe present invention is deposited may comprise a coupling agent, whichmay, for example, improve the adhesion of the second layer to the firstlayer. Examples of coupling agents suitable for this purpose include,without limitation, the materials described in U.S. Pat. No. 6,165,256at col. 8, line 27 to col. 9, line 8, incorporated herein by reference.

In certain embodiments, the amount of coupling agent that is present inthe liquid composition from which the second layer of the multi-layercoating is deposited ranges from 0.01 to 1 percent by weight, such as0.01 to 0.5 percent by weight based on the total weight of thecomposition. In these embodiments, the amount of coupling agent that maybe present in the liquid, composition can range between any combinationof the recited values, inclusive of the recited values.

In certain embodiments, the liquid composition from which the secondlayer of the multi-layer coatings of the present invention is depositedmay comprise a surface active agent, which may, for example, aid inimproving the wetting properties of the composition when thatcomposition is applied over the first layer. Examples of surface activeagents suitable for use in the present invention include, withoutlimitation, the materials identified in U.S. Pat. No. 6,610,777 at col.37, line 22 to col. 38, line 60 and U.S. Pat. No. 6,657,001 at col. 38,line 46 to col. 40, line 39, which are both incorporated herein byreference.

In certain embodiments, the amount of surface active agent that ispresent in the liquid composition from which the second layer of themulti-layer coating is deposited ranges from 0.01 to 3 percent byweight, such as 0.01 to 2 percent by weight, or, in other embodiments,0.1 to 1 percent by weight based on the total weight of solids in thecomposition. In these embodiments, the amount of surface active agentthat may be present in the liquid composition can range between anycombination of the recited values, inclusive of the recited values.

In certain embodiments, the liquid composition from which the secondlayer of the multi-layer coating is applied also comprises a cleaningcomposition. Suitable cleaning compositions includes those materialsthat comprise a surfactant, a solvent system, water, and a pH adjustingagent, such as acetic acid or ammonia. A suitable cleaning compositionis disclosed in U.S. Pat. No. 3,463,735, which discloses a cleaningcomposition comprising a solvent system comprising a low boiling solventsuch as isopropanol, and a moderately high boiling solvent, such as a C₁to C₄ alkylene glycol alkyl ether having a total of 3 to 8 carbon atoms.Suitable commercially available cleaning compositions include WINDEX®,commercially available from SC Johnson and Son, Inc. As a result,certain embodiments of the present invention are directed to liquidcompositions that are hydrophilic and comprise (a) an essentiallycompletely hydrolyzed organosilicate, and (b) a cleaning composition.Certain embodiments of such compositions also comprise a photocatalyticmaterial.

In certain embodiments, the cleaning composition is present in suchliquid compositions in an amount of at least 10 weight percent, such asat least 20 weight percent, or, in some cases at least 25 weightpercent, with weight percent being based on the total weight of theliquid composition.

If desired, the liquid composition from which the second layer of themulti-layer coatings of the present invention is deposited can compriseother optional coatings materials well known to those skilled in thecoatings art.

The liquid composition from which certain embodiments of the secondlayer of the multi-layer coatings of the present invention is depositedcan be made by a variety of methods. In certain cases, the compositionis prepared by (i) providing a hydrophilic material comprising anessentially completely hydrolyzed organosilicate, wherein the pH of thehydrophilic material is no more than 3.5; (ii) providing a sol or pastecomprising a photocatalytic material dispersed in a diluent, wherein thepH of the sol is no more than 3.5; and (iii) mixing the hydrophilicmaterial provided in (i) with the sol or paste provided in (ii) todisperse the photocatalytic material in the hydrophilic material. It hasbeen found that liquid compositions made by this method can be stablefor over 12 months with little or no agglomeration or precipitation. ThepH values reported herein can be determined using an ACCUMET pH metercommercially available from Fisher Scientific.

In certain cases, the liquid composition from which the second layer ofthe multi-layer coatings of the present invention is deposited isproduced by providing a hydrophilic material comprising an essentiallycompletely hydrolyzed organosilicate, wherein the pH of the hydrophilicmaterial is no more than 3.5 or, in some cases, from 1.3 to 3.5 or, inyet other cases, 3.0 to 3.5. In certain embodiments, such a hydrophilicmaterial is obtained by first providing an essentially completelyhydrolyzed organosilicate wherein the pH of the hydrophilic material isgreater than the desired pH and then adding acid to the hydrophilicmaterial until the pH of the hydrophilic material is no more than 3.5or, in some cases from 1.3 to 3.5 or, in yet other cases, 3.0 to 3.5.For example, as mentioned earlier, the hydrophilic material may comprisethe MSH-200 and/or Shinsul. Flow MS-1200 silicates, which are typicallyprovided by the supplier at a pH of 3.5 to 4.5.

In certain embodiments, the hydrophilic material may be diluted with adiluent, such as water or an organic solvent, before the addition ofacid to, for example, reduce the solids content of the hydrophilicmaterial, thereby allowing for the formation of thinner films.

Acids that may be added to the hydrophilic material to adjust the pHthereof include both inorganic and organic acids. Suitable inorganicacids include, without limitation, hydrochloric acid, sulfuric acid,nitric acid and phosphoric acid, among others. Suitable organic acidsinclude acetic acid, dichloroacetic acid, trifluoroacetic acid,benzenesulfonic acid, toluenesulfonic acid, xylenesulfonicacid,ethylbenzenesulfonic acid, benzoic acid, phthalic acid, maleic acid,formic acid and oxalic acid, among others.

In certain cases, the liquid composition from which the second layer ofthe multi-layer coating is deposited is produced by providing a sol orpaste comprising a photocatalytic material dispersed in a diluent,wherein the pH of the sol or paste is no more than 3.5 or, in somecases, from 1.3 to 3.5 or, in yet other cases 3.0 to 3.5. In certainembodiments, the pH of the sol or paste is substantially the same asthat of the hydrophilic material. In certain embodiments, such a sol orpaste is obtained by first providing such a sol or paste wherein the pHthereof is greater than the desired pH and then adding acid to the solor paste until the pH of the sol or paste is no more than 3.5 or in somecases from 1.3 to 3.5 or, in yet other cases, 3.0 to 3.5. For example,as mentioned earlier, the photocatalytic material used in certainembodiments of the liquid compositions from which the second layer ofthe multi-layer coatings of the present invention is deposited maycomprise a sol of titanium dioxide available from Showa DenkoCorporation under the names NTB-1 and/or NTB-13, wherein the solcomprises brookite-type titanium oxide particles or a mixture ofbrookite-type with anatase-type and/or rutile-type titanium oxideparticles dispersed in water. NTB-1 and NTB-13 are typically provided bythe supplier at a pH of 2 to 4.

Acids that may be added to the sol or paste comprising thephotocatalytic material to adjust the pH thereof include both theinorganic and organic acids described earlier, among others. In certainembodiments, the acid that is added to the sol or paste comprising thephotocatalytic material is the same acid that is added to thehydrophilic material as described earlier.

The liquid compositions from which the second layer of the multi-layercoatings of the present invention are deposited can be made by mixingthe hydrophilic material provided as described above with the sol orpaste provided as described above to disperse the photocatalyticmaterial in the hydrophilic material. The mixing step is notparticularly limited and may be accomplished by any conventional mixingtechnique known to those of skill in the art so long as the mixingresults, in a dispersion of the photocatalytic material in thehydrophilic material. As a result, certain embodiments of the presentinvention are directed to multi-layer coatings, wherein the second layeris deposited from a liquid composition having a pH of no more than 3.5,such as 1.3 to 3.5, or, in some cases, 3.0 to 3.5.

In other cases, the liquid composition from which the second layer ofthe multi-layer coatings of the present invention is deposited isprepared by (i) providing a hydrophilic material comprising anessentially completely hydrolyzed organosilicate, wherein the pH of thehydrophilic material is from 7.0 to 8.5; (ii) providing a sol or pastecomprising a photocatalytic material dispersed in a diluent, wherein thepH of the sol or paste is from 7.0 to 8.5; and (iii) mixing thehydrophilic material provided in (i) with the sol or paste provided in(ii) to disperse the photocatalytic material in the hydrophilicmaterial.

In certain cases, the compositions from which the second layer of themulti-layer coatings of the present invention is deposited is producedby providing a hydrophilic material that comprises an essentiallycompletely hydrolyzed organosilicate, wherein the pH of the hydrophilicmaterial is from 7.0 to 8.5, such as 7.0 to 8.0 or, in some cases, 7.5to 8.0. In certain embodiments, such a hydrophilic material is obtainedby first providing an essentially completely hydrolyzed organosilicatewherein the pH of the hydrophilic material is less than the desired pHand then adding a base to the hydrophilic material until the pH of thehydrophilic material is from 7.0 to 8.5, such as 7.0 to 8.0 or, in somecases, 7.5 to 8.0.

In certain embodiments; the hydrophilic material may be diluted with adiluent, such as water or an organic solvent, before the addition of thebase to, for example, reduce the solids content of the hydrophilicmaterial thereby allowing for the formation of thinner films.

Materials that may be added to the hydrophilic material to adjust the pHthereof include both organic bases and inorganic bases. Specificexamples of bases which may be used to raise the pH of the hydrophilicmaterial include, without limitation, alkali metal hydroxides, such assodium hydroxide, potassium hydroxide and lithium hydroxide; ammoniumhydroxide; quaternary ammonium hydroxides, such as tetraethyl ammoniumhydroxide and tetraethanol ammonium hydroxide; ammonia; amines such as,triethylamine and 3-(diethylamino)-propan-1-ol; tertiary sulfoniumhydroxides, such as trimethyl sulfonium hydroxide and triethyl sulfoniumhydroxide; quaternary phosphonium hydroxides such as, tetramethylphosphonium hydroxide and tetraethyl phosphonium hydroxide;organosilanolates, such as tripotassium γ-aminopropylsilantriolate,tripotassium N-(β-aminoethyl)-γ-aminopropylsilantriolate, dipotassiumdimethylsilandiolate, potassium trimethylsilanolate,bis-tetramethylammonium dimethylsilandiolate, bis-tetraethylammoniumdimethylsilandiolate, and tetraethylammonium trimethylsilanolate; sodiumacetate; sodium silicate; ammonium bicarbonate; and mixtures thereof.

In certain cases, the liquid composition from which the second layer ofthe multi-layer coatings of the present invention is deposited isprepared by providing a sol or paste that comprises a photocatalyticmaterial dispersed in, a diluent, wherein the pH of the sol or paste isfrom 7.0 to. 8.5,such as 7.0 to 8.0 or, in some embodiments, from 7.5 to8.0. In certain embodiments, the pH of the sol or paste is substantiallythe same as that of the hydrophilic material. In certain embodiments,such a sol or paste is obtained by first providing such a sol or pastewherein the pH thereof is less than the desired pH and then adding analkali material to the sol or paste until the pH thereof is from 7.0 to8.5, such as 7.0 to 8.0 or, in some cases from 7.5 to 8.0.

Bases that may be added to the sol or paste comprising thephotocatalytic material to adjust the pH thereof include the inorganicand organic bases described earlier, among others. In certainembodiments, the base that is added to the sol or paste comprising thephotocatalytic material is the same base that is added to thehydrophilic material.

The liquid compositions from which the second layer of the multi-layercoatings of the present invention is deposited can be made by mixing thehydrophilic material as described above with the sol or paste providedas described above to disperse the photocatalytic material in thehydrophilic material. The mixing step is not particularly limited andmay be accomplished by any conventional mixing technique known tothose:of skill in the art, so long as the mixing results in a dispersionof the photocatalytic material in the hydrophilic material. As a result,certain embodiments of the present invention are directed to multi-layercoatings, wherein the second layer is deposited from a liquidcomposition having a pH of 7.0 to 8.5, such as 7.0 to 8.0, or, in somecases, 7.5 to 8.0.

Referring now to FIGS. 2 and 3, there is seen (i) a schematiccross-sectional view in an enlarged scale of certain embodiments of thesecond layer of a multi-layer coating of the present invention, and (ii)a micrograph illustrating an embodiment of a second layer of amulti-layer coating of the present invention, respectively. As isapparent from FIGS. 2 and 3, in certain embodiments, the second layer ofthe multi-layer coatings of the present invention are deposited from aliquid composition wherein the photocatalytic material is dispersedthroughout the hydrophilic binder. In these embodiments, the secondlayer of the multi-layer coating comprises a photocatalytic material inthe form of nano-sized photocatalytic particles 10 (in these particularexamples, the particles have an average crystalline diameter no morethan 20 nanometers), which are relatively uniformly dispersed throughoutthe hydrophilic binder 20. In particular, as shown in FIG. 3, theparticles 10 are non-agglomerated, i.e., all-or nearly all of theparticles are encapsulated by, and separated by, the binder rather thanbeing combined to each other. While not being limited by any theory itis believed that, by controlling the pH of the hydrophilic material andthe sol or paste of photocatalytic material prior to their combination,the photocatalytic particles can be well dispersed in the hydrophilicmaterial, such that agglomeration is prevented, which results in aliquid composition of low turbidity. Thus, in certain embodiments of thepresent invention, the second layer of the multi-layer coating isdeposited from a liquid composition having low turbidity.

One advantage of the liquid compositions from which the second layer ofthe multi-layer coatings of the present invention is deposited, and/orthe methods of their production, is that they may form stableone-package liquid compositions. Therefore, in certain embodiments, thesecond layer of the multi-layer coating of the present invention isdeposited from a one-pack liquid composition. As used herein, the term“one-pack liquid composition” refers to a liquid composition wherein thecomponents comprising the liquid composition are stored together in asingle container.

The one-pack liquid compositions that may be used to form the secondlayer in the multi-layer coatings of the present invention comprise atleast two components, including the previously discussed photocatalyticmaterials and hydrophilic binders. In addition, such one-pack liquidcompositions have a shelf-life of at least 3 months. As used herein, theterm “shelf-life” refers to the amount of time between when thecomponents are combined in a single container and the occurrence ofprecipitation or agglomeration to an extent that the turbidity of thecomposition increases such that the composition can no longer form a lowhaze film. In certain embodiments, the one-pack liquid compositions havea shelf-life of at least 3 months or, in certain other embodiments, atleast 6 months, or, in some cases, at least 12 months.

In certain embodiments, the liquid composition from which the, secondlayer of the multi-layer coatings of the present invention is depositedhas a turbidity of no more than 600 NTU or, in some cases, not more than400 NTU (Nephelometric Turbidity Units) after 3 months, 6 months, or, insome cases, 12 months. The turbidity values reported herein can bedetermined by a Turbidimeter, Model DRT-100D, manufactured by ShabanManufacturing Inc, H. F. Instruments Division using a sample cuvette of28 mm diameter by 91 mm in length with a flat bottom. Moreover, incertain embodiments, the second layer of the multi-layer coatings of thepresent invention have low haze. As used herein, “low haze” means thatthe film has a haze of no more than 0.3%. The haze values reportedherein can be determined with a haze meter, such as a Hazegard® ModelNo. XL-211, available from Pacific Scientific Company, Silver Spring,Md.

The present invention is also directed to methods of applying amulti-layer coating to a substrate comprising the steps of (1) applyingto a substrate a first layer comprising an inorganic oxide network; (2)applying onto at least a portion of the first layer a liquid compositionfrom which a second layer is deposited, wherein the composition of thesecond layer is hydrophilic and comprises an essentially completelyhydrolyzed organosilicate; and (3) curing the second layer.

In these methods, the first layer comprises an inorganic oxide networkand the composition from which such a layer is deposited may be appliedto the substrate by any of the methods used in coating technology suchas, for example, spray coating, roll coating, dipping, spin coating,flow coating, brushing, and wiping, among others. After application,such a composition may be cured. For example, the composition from whichthe first layer of the multi-layer coating is deposited may be appliedto the substrate as a solution of solids in an appropriate solvent, suchas water, an organic solvent, or a mixture thereof. The solvent may thenbe evaporated and the coating cured by heating to elevated temperatures,such as 80° to 130° C. for 1 to 1.6 hours.

In these methods of the present invention, the liquid composition fromwhich the second layer is deposited may be applied to the substrate byany of the methods used in coating technology such as those mentionedearlier.

In these methods of the present invention, the second layer is cured,i.e., dried, after it is applied onto the first layer. Though not beingbound by any theory, it is believed that, upon cure, some of the silanolgroups of the essentially completely hydrolyzed binder are condensed sothat Si—O—Ti bonds are formed within the composition. It is believedthat the presence of these groups enhance the durability of the secondlayer in the multi-layer coatings of the present invention, as describedin more detail below.

The liquid composition from which the second layer of the multi-layercoatings of the present invention is deposited may be self-curing, suchthat the composition may cure without the aid of any cure catalyst.Moreover, the liquid composition from which the second layer of themulti-layer coating of the present invention is deposited may, forexample, be cured at ambient temperatures. In other words, curing of theliquid composition of the second layer may be accomplished by allowingthe composition to stand in air, i.e., air drying. According to certainembodiments of the present invention, the liquid composition is cured byexposing it to air for 2 to 3 hours at 25° C. to achievesuperhydrophilicity and 16 hours to achieve long-term durability. Suchliquid compositions may also be cured by heat drying. For example,according to certain embodiments of the present invention, the secondlayer is cured by exposing it to air for 3 to 5 minutes and then forcedrying it at 80° C. to 100° C. for at least 3 seconds.

The multi-layer coatings of the present invention may be applied topolymeric, ceramic, concrete, cement, glass, wood, paper, or metalsubstrates, composite materials thereof, or other materials, includingpainted substrates. In certain particular embodiments, the multi-layercoatings of the present invention are applied to a polymeric substrate.In certain embodiments, such polymeric substrates may comprise a solidtransparent or optically clear solid material, such as is disclosed inU.S. Pat. No. 6,042,737at col. 6, line 66 to col. 8, lines 34, which isincorporated herein by reference. In certain embodiments, such polymericsubstrates may comprise a photochromic material, such as is disclosed inU.S. Pat. No. 6,042,737 at col. 8, line 35 to col. 10, line 19, which isincorporated herein by reference.

Specific examples of articles upon which the multi-layer coatings of thepresent invention may be applied include, without limitation, windows;windshields on automobiles aircraft, watercraft and the like; indoor andoutdoor mirrors; lenses, ;eyeglasses or other optical instruments;protective sports goggles; masks; helmet shields; glass slides of frozenfood display containers; glass covers; buildings walls; building roofs;exterior tiles on buildings; building stone; painted steel plates;aluminum panels; window sashes; screen doors; gate doors; sun parlors;handrails; greenhouses; traffic signs; transparent soundproof walls;signboards; billboards; guardrails; road reflectors; decorative panels;solar cells; painted surfaces on automobiles watercraft, aircraft, andthe like; painted surfaces on lamps; fixtures, and other articles; airhandling systems and purifiers; kitchen and bathroom interiorfurnishings and appliances; ceramic tiles; air filtration units; storeshowcases; computer displays; air conditioner heat exchangers;high-voltage cables; exterior and interior members of buildings; windowpanes; dinnerware; walls in living spaces, bathrooms, kitchens, hospitalrooms, factory spaces, office spaces, and the like; sanitary ware, suchas basins, bathtubs, closet bowls, urinals, sinks, and the like; andelectronic equipment, such as computer displays.

In certain embodiments, the liquid composition from which the secondlayer of the multi-layer coatings of the present invention is depositedcan have a very low solids content, approximately 1 percent by weighttotal solids based on the total weight of the composition. Consequently,such a liquid composition can be applied at extremely small filmthicknesses. In particular, according to certain embodiments of thepresent invention; the liquid composition is applied onto at least aportion of the first layer in the form of a thin film that has a dryfilm thickness of no more than 200 nanometers (0.2 micrometers) or, insome embodiments, 10 to 100 nanometers (0.01 to 0.1 micrometers), in yetother embodiments of the present invention, 20 to 60 nanometers (0.02 to0.06 micrometers). Application of the second layer of the multi-layercoatings of the present invention at such low film thickness can beparticularly advantageous in providing an optical thin film withoutnecessarily matching the refractive index of the composition to that ofthe first layer.

As mentioned previously, the liquid composition from which the secondlayer of the multi-layer coatings of the present invention is depositedis initially hydrophilic, that is, upon application, and prior toexcitation of any photocatalyst that may be present in the compositionof the second layer, the second layer exhibits an affinity to water.This initial hydrophilicity can be illustrated by an initial watercontact angle of no more than 20° or, in some embodiments, no more than150°, or, in yet other embodiments, no more than 10°. Upon excitation ofthe photocatalytic material, if any, the second layer of the multi-layercoatings of the present invention can be rendered “super-hydrophilic,”that is, following excitation of the photocatalyst, the second layer ofthe multi-layer coatings of the present invention can exhibit a watercontact angle of less than 5°, even as little as 0°.

The means that may be used for exciting the photocatalyst, if any ispresent in the liquid composition from which the second layer isdeposited, depends on the photocatalytic material used in thecomposition. For example, materials that are photoexcited upon exposureto visible light, such as the brookite form of titanium dioxide, as wellas nitrogen or carbon doped titanium dioxide, may be exposed to anyvisible light source including any radiation of a wavelength of at least400 nanometers. On the other hand, the anatase and rutile forms oftitanium dioxide, tin oxide, and zinc oxide can be photoexcited byexposure UV radiation of a wavelength of less than 387 nanometers, 413nanometers, 344 nanometers, and 387 nanometers, respectively. SuitableUV radiation sources for photoexciting such photocatalysts include,without limitation, a UV lamp, such as that sold under the tradenameUVA-340 by the Q-Panel Company of Cleveland, Ohio, having an intensityof 28 watts per square meter (W/m²) at the coating surface.

In certain embodiments, the multi-layer coatings of the presentinvention exhibit a photoactivity of at least 0.5 cm⁻¹min⁻¹, such as, atleast 1.0 cm⁻¹min⁻¹. Photoactivity can be evaluated as described in U.S.Pat. No. 6,027,766 at col. 11, line 1 to col, 12, line 55, which isincorporated herein by reference.

In certain embodiments, the multi-layer coatings of the presentinvention are rendered superhydrophilic upon exposure to sunlight for aperiod of 1to 2 hours. Alternatively, the multi-layer coatings of thepresent invention may be rendered superhydrophilic upon exposure to UVradiation of an intensity of 28 W/m for 1 hour.

As discussed previously, the multi-layer coatings of the presentinvention can exhibit very favorable hydrophilic, anti-static and/oranti-bacterial properties, among others. Because they are hydrophilic,the multi-layer coatings of the present invention may exhibitadvantageous self-cleaning, anti-fouling, and/or anti-foggingproperties. The present invention, therefore, is also directed tomethods for improving the anti-fouling, self-cleaning, easy-to-clean,and/or anti-fogging properties of an article, wherein the articlecomprises a surface having a coating layer comprising an inorganic oxidenetwork deposited thereon, the method comprising: (1) applying to atleast a portion of the surface a liquid composition comprising anessentially completely hydrolyzed organosilicate; and (2) curing thecomposition applied in step (1).

Another feature of the multi-layer coatings of the present invention isthat they may result in a second layer that is particularly durable. Thesurprising durability of such coatings can be measured in terms of theability of the film surface to maintain a contact angle over time underaccelerated weather conditions. The lower the degree of contact anglethat can be maintained by the sample tested over time or number ofwiping cycles, the more durable the film. Simulating weathering of thefilm can be obtained via weathering chambers, which include theCleveland Condensing Cabinet (CCC) and QUV Tester (products of TheQ-Panel Company, Cleveland, Ohio).

In certain embodiments, the photocatalytic material is present in theliquid composition from which the second layer of the multi-layercoatings of the present invention is deposited in an amount sufficientto produce a multi-layer coating that maintains:a contact angle of lessthan 10 degrees, such as less than 5 degrees and/or a photoactivity of 3cm⁻¹min⁻¹ after exposure to a CCC chamber for 4000 hours, where the CCCchamber is operated at a vapor temperature of 140° F. (60° C.) in anindoor ambient environment which results in constant water condensationon the test surface. Indeed, as illustrated by the Examples herein, itwas discovered that the inclusion of a photocatalytic material incertain embodiments of such compositions produced coatings exhibitingdramatically improved durability as compared to compositions containinga hydrophilic binder of the type described herein but no photocatalyticmaterial. As illustrated by FIG. 4, in certain embodiments, thephotocatalytic material can be included in the composition from whichthe second layer of the multi-layer coatings of the present invention isdeposited in an amount sufficient to yield a multi-layer coating thatmaintains its initial water contact angle (i.e., the water contact angleis within 4 degrees of the initial water contact angle, wherein “initialwater contact angle” refers to the water contact angle observed afterexposure to UV light for 2 hours as described in the Examples but beforeexposure to the CCC chamber) even after exposure of the coating to a CCCchamber for 4000 hours as described above, whereas the absence of aphotocatalytic material yielded a coating that could not maintain itsinitial water contact angle after approximately 2000 to 3000 hours ofsuch exposure. Indeed, the Examples illustrate that in the absence of aphotocatalytic material the contact angle of the surface increased tonearly three times the initial contact angle a exposure in a CCCfor,3500 hours. Without being bound by any theory the inventors believethat this surprising result can be attributed to a partial crosslinkingof the photocatalytic material with the organosilicate which yieldsSi—O—Ti bonds in the coating. The inventors believe that somephotocatalytic material takes part in such crosslinking, while somephotocatalytic material remains available for photocatalytic activationeven after 4000 hours of CCC exposure.

In certain embodiments, the multi-layer coatings of the presentinvention may maintain a contact angle of 5 to 6 degrees after exposureto 650 hours in a QUV Tester equipped with fluorescent tubes (B313nanometers) at black panel temperature of 650 to 70° C. and 4 hourscondensing humidity at 50° C.

Illustrating the invention are the following examples, which, however,are not to be considered as limiting the invention to their details.Unless otherwise indicated, all parts and percentages in the followingexamples, as well as throughout the specification, are by weight.

EXAMPLES Example 1 Preparation of a Hydrolyzed Organosilicate Binder

An acid hydrolysis catalyst solution, referred to herein as solution“A”, was prepared by adding 7,000 grams of deionized water to a clean,dry 2 gallon container. With stirring 1.0 gram of 70% nitric acid wasadded and set aside.

15.5 grams (˜0.10 moles) of 98% TMOS (tetramethoxysilane) representing˜6 grams of SiO₂ was added to a clean, dry 1 liter glass beaker. 3.6grams of solution A (˜0.20 moles of H₂O) was slowly added to the TMOS,controlling the exotherm by using an ice bath to maintain thetemperature below 25° C. Upon the completion of the addition of solutionA, this partially hydrolyzed silane solution was held for one hour at25° C. In a separate clean, dry beaker, 290.5 grams of ethanol and 290.5grams of deionized water were mixed and then added to the partialhydrolyzate with stirring, after the one hour hold time. Then the pH ofthe diluted silane solution (pH˜5) was adjusted to pH˜3.9 by adding 0.80grams of glacial acetic acid with stirring. The resultant 1% SiO2 bindersolution was allowed to fully hydrolyze overnight with stirring.

Application on test panels with above solution show good wetting with nooptical flaws and passes 50 flood/dry cycles maintaining goodhydrophilicity.

Example 2 Preparation of a Hydrolyzed Organosilicate Binder

15.5 grams (˜0.10 moles) of 98% TMOS representing ˜6 grams of SiO₂ and3.6 grams of anhydrous methanol (cosolvent) were added to a clean, dry 1liter glass beaker. 3.6 grams of solution A (˜0.20 moles of H₂O) wasslowly added to the TMOS solution, controlling the exotherm by the rateof addition of solution A. The peak temperature attained during theaddition was 33° C. Upon the completion of the addition of solution A,this partially hydrolyzed silane solution was held for one hour at ˜25°C. In a separate clean, dry beaker, 287 grams of ethanol and 290.5 gramsof deionized water was mixed and then added to the partial hydrolyzatewith stirring, after the one hour hold time. Then, the pH of the dilutedsilane solution. (pH˜5) was adjusted to pH˜3.9 by adding 0.80 grams ofglacial acetic acid with stirring. The resulting. 1 % SiO₂ bindersolution was allowed to fully hydrolyze overnight with stirring.

Application on test panels with above solution show dewetting problemswith mottling. The test results suggest that the inclusion of cosolventprovided for a more efficient hydrolysis and corresponding condensationto form higher molecular weight oligomers which demonstrated theobserved behavior upon application.

Example 3 Preparation of a Hydrolyzed Organosilicate Binder

15.5 grams (˜0.10 moles) of 98% TMOS (tetramethoxysilane) representing˜6 grams of SiO₂ was added to a clean, dry 1 liter glass beaker. 3.6grams of solution A (˜20 moles of H₂O) was slowly added to the TMOS,controlling the exotherm by the rate of addition of solution A. The peaktemperature attained during the addition was 40° C. Upon the completionof the addition of solution A, this partially hydrolyzed silane solutionwas held for one hour at −25° C. In a separate clean, dry beaker, 290.5grams of ethanol and 290.5 grams of deionized water were mixed and thenadded to the partial hydrolyzate with stirring, after the one hour holdtime. Then, the pH of the diluted silane solution (pH˜5) was adjusted topH˜3.9 by adding 0.80 grams of glacial acetic acid with stirring. The 1%SiO2 binder solution was allowed to fully hydrolyze overnight withstirring.

Application on test panels with above solution show dewetting problemswith mottling. The test results suggest that by not controlling theexotherm and allowing the temperature of the hydrolysis to reach ˜40°C., resulted in a much higher degree of condensation to form highermolecular weight oligomers which demonstrated the observed behavior uponapplication.

Example 4 Preparation of a Hydrolyzed Organosilicate Binder

Methanol and deionized water were mixed at 1:.1 (w:w) ratio understirring, The mixture was cooled to room temperature. 10.0 g of MS-51silicate solution (Mitsubishi Chemical Corporation, Tokyo, Japan) wascharged into a glass reactor, followed by addition of 504.8 g of thepre-mixed methanol/water solvent mixture as one portion. The solutionwas stirred at 20-22° C. for 15 minutes. Then, 5.2 g of glacial aceticacid was added into the reactor under agitation. The solution mixturewas kept stirred at ambient for additional 24 hours. The final SiO₂content of the solution was 1 % with a pH of 3.5.

Example 5 Preparation of a Hydrolyzed Organosilicate Binder

1-propanol and deionized water were mixed at 1:1 (w:w) ratio understirring. The mixture was cooled to room temperature. In a separate,container, acetic acid solution was prepared by diluting 10.0 g ofglacial acetic acid with 90.0 g of 1-propanol/water solvent mixture. 5.0g of MS-51 silicate solution was charged into a glass reactor, followedby addition of 253.7 g of the pre-mixed 1-propanol/water solvent mixtureas one portion. The solution was stirred at 2-22° C. for 15 minutes.Then 1.4 g of pre-prepared acetic acid solution was added into thereactor under agitation. The solution mixture was kept stirred atambient for additional 24 hours. The final SiO₂ content of the solutionwas 1% with a pH of 4.1.

Example 6 Preparation of Liquid Compositions

Liquid compositions A through G in Table 1 were prepared as follows.Charge I was prepared in a one liter glass vessel equipped with amagnetic stirrer. Charge I was prepared by adding the binder material tothe vessel and then adding deionized water to the vessel underagitation. The pH of the mixture was adjusted to 1.8 by adding 2Nhydrochloric acid under agitation until the desired pH was achieved.

Charge II was prepared in a 4 oz. glass container equipped with amagnetic stirrer. Titania sol was added to this vessel and the pH wasadjusted to 1.8 by adding 2N hydrochloric acid under agitation until thedesired pH was achieved. Charge II was then added under agitation toCharge I to produce the hydrophilic compositions A through G. TABLE 1Silicate/TiO₂ Titania Composition Weight Ratio Binder¹ DI Water TitaniaSol² Sol³ A 0.5/0.3 500 g  480 g   20 g — B 0.5/0.3 500 g  480 g   20 g— C 0.4/0.24  40 g 58.4 g  1.6 g — D 0.31/0.19  31 g 67.7 g 1.27 g — E0.25/0.25  25 g 73.3 g 1.67 g — F 0.9/0.1  47 g  2.3 g 0.33 g — G0.5/0.3  25 g 24.5 g — 0.5 g¹MSH-200 hydrolyzed organosilicate (1% solids) commercially availablefrom Mitsubishi Chemical Corporation, Tokyo, Japan.²NTB-1 titania sol commercially available from Showa Denko K.K., Tokyo,Japan.³STS-01 titania sol commercially available from Ishihara Sangyo KaishaLtd.

Example 7 Float Glass Test Substrates

The surface of 9″12″ float glass test substrates were prepared bycleaning the substrate with a diluted Dart 210 solution (commerciallyavailable from. Madison Chemical Co., Inc.) prepared by dilutingconcentrated Dart 210 with deionized water so that the solution had aconcentration of 5% to 10% Dart 210. The substrate was then rinsed withhot tap water and then deionized water. The test substrate was sprayedwith Windex® and wiped dry with a paper towel (Kaydry® commerciallyavailable from Kimberly-Clark Corp.).

The liquid compositions of Example 6 were each applied to a testsubstrate by wipe application using a BLOODBLOC Protective Pad,commercially available from Fisher Scientific. The pad was wrappedaround the foam applicator. Then, 1.5 grams of the hydrophiliccomposition was applied to the pad using an eye dropper or plasticbottle with a dropper top. The compositions were then applied bycontacting the wet pad with the glass test substrate with straight,slightly overlapping strokes. After application, the substrate wasallowed to dry at room temperature for at least 2 prior to testing.Results are summarized in Table 2 TABLE 2 Ti PCA Surface ResistivityComposition (μg/cm²)¹ (cm⁻¹min⁻¹)² (ohms/cm²)³ Haze⁴ A 1.2 3.9 3.84 ×10⁹ 0.1% B 2.3 8.1 6.25 × 10⁸ 0.2% C 0.7 2.1 — — D 0.5 1.3 — — E 0.7 2.6— — F 0.4 0.6 — — G 1.9 5.5 — —¹Sample analyzed using X-ray fluorescence analysis.²Photocatalytic activity was evaluated as described in U.S. Pat. No.6,027,766 at col. 11, line 1 to col, 12, line 55.³Surface resistivity was evaluated with an ACL Statitide Model 800Megohmeter using either (1) large extension probes placed 5 millimetersapart at several locations on the sample, or (2) the meter's onboardprobes spaced 2¾ inches apart at several locations# on the sample.⁴Haze was evaluated with a Hazegard ® Model No. XL-211 haze meter,available from Pacific Scientific Company, Silver Spring, Md.

Durability Testing-Test 1

Test substrates coated with liquid compositions A and B were placed in aCleveland Condensation Chamber operating at 140° F. (60° C.). Each testsubstrate was removed from the chamber weekly and tested to determinethe water contact angle. The photoactivity of the composition wasdetermined by measuring the water contact angle difference before andafter exposure of the substrate to UV light. The exposure interval was 2hours to a UVA-340 lamp supplied by the Q-Panel Company of Cleveland,Ohio or direct sunlight. The water contact angles reported were measuredby the sessile drop method using a modified captive bubble indicatormanufactured by Lord Manufacturing, Inc., equipped with GartnerScientific goniometer optics. The surface to be measured was placed in ahorizontal position, facing upward, in front of a light source. Asessile drop of water was placed on top of the surface in front of thelight source so that the profile of the sessile drop could be viewed andthe contact angle, measured in degrees through the goniometer telescopewhich is equipped with circular protractor graduations. Results aresummarized in Table 3. TABLE 3 Composition A Contact Composition B AngleContact Contact Angle Contact Angle Hours in Before Angle After BeforeAfter CCC Exposure Exposure Exposure Exposure 0 20 3 12 3 498 14 3 12 31062 38 3 37 3 1535 32 3 27 3 2221 18 4 9 3 2573 30 3 26 3 2975 30 5 334 3565 — — 30 5 4040 — — 19 4

Durability Testing-Test 2

The durability of test substrates coated with liquid compositions Athrough G was tested by measuring the water contact angle after exposureto UV light as described above but prior to placement in the ClevelandCondensation Chamber The same substrates were then placed in the CCC asdescribed above-for at least 4000 hours and then removed. The substrateswere then exposed to UV light as described above and tested by measuringthe water contact angle. Results are summarized in Table 4. TABLE 4Contact Angle Before CCC Contact Angle After Composition Exposure 4000Hours CCC A 3 5 B 3 4 C 5 4 D 5 3 E 6 2 F 5 9 G 3 3

Durability Testing-Test 3

The durability of test substrates coated with compositions of thepresent invention was also compared to substrates coated withcompositions comprising hydrophilic organosilicate binder but no thephotocatalytic material. Hydrophilic compositions B and F of Example 6as well as a similar composition having a binder to titanium dioxideratio of 95/0.5 (composition J) were placed in the ClevelandCondensation Chamber as described above a periodically removed andexposed to UV light as described above. Comparative composition A wasShinsui Flow MS-1 200, available from Dainippon Shikizai, Tokyo, Japanand comparative composition B was MSH-200, available from MitsubishiChemical Corporation, Tokyo, Japan. The test substrates were tested forwater contact angle as described above. Results are illustrated in FIG.4.

Example 8 Preparation of Liquid Compositions

Liquid compositions H and I were prepared in the manner described inExample 6 except that WINDEX was included in the composition in theamount identified in Table 5 and the Binder/TiO₂Weight Ratio was asadjusted as set forth in Table 5. The durability of these compositionswas then analyzed in the manner described in Durability Testing-Test 1.Results are set forth in Table 6. TABLE 5 Silicate/TiO₂ Amount of Amountof Composition Weight Ratio Binder/TiO₂ ¹ WINDEX H 0.35/0.25 30 g 8.91 gI 0.35/0.25 30 g 6.26 g

TABLE 6 Composition H Composition I Contact Contact Contact ContactHours in Angle Before Angle After Angle Before Angle After CCC ExposureExposure Exposure Exposure 0 4 4 5 4 330 27 2 21 2 834 19 2 31 2 2390 263 23 5 3374 18 3 16 3 4022 38 4 32 11

Example 9 Turbidity of Liquid Compositions

Liquid compositions K, L, M, and O were prepared in the manner describedin Example 6 except that the pH was adjusted to the value set forth inTable 7 and the Binder/TiO₂Weight Ratio was as adjusted, as set forth inTable 7. Liquid compositions N, P, and Q were prepared in a mannersimilar to Example 6, except that the pH of Charge I was not adjusted,and Charge II was a mixture of the titania sol and deionized water in anamount sufficient to dilute the titania sol from 15% solids to 2% solidswith deionized water. The pH of Charge II was not adjusted and Charge IIwas added to Charge I to make the liquid composition. The turbidity ofthese compositions, was then analyzed over time by a Turbidimeter, ModelDRT-100D, manufactured by Shaban Manufacturing Inc, H. F. InstrumentsDivision using a sample cuvette of 28 mm diameter by 91 mm in lengthwith a flat bottom. Results are set forth in Table 7. TABLE 7 Turbidity(NTU) Silicate/TiO₂ 1 3 Composition Weight Ratio pH Initial month months6 months K 0.5/0.3 1.96 490 558 569 652 L 0.5/0.3 1.57 438 552 567 653 M0.35/0.2  1.8 321 383 393 442 N 0.35/0.2  3.25 454 412 385 425 O 0.4/0.25 1.8 415 488 511 573 P 0.5/0.1 3.1 145 143 145 153 Q 0.9/0.13.11 149 143 145 162

Example 10 Fogging Resistance on a Plastic Lens

This example is intended to illustrate the anti-fogging properties ofthe present invention. Thermoplastic polycarbonate lenses that werepreviously coated by the supplier with a non-tintable hardcoat (Gentex®PDQ®, commercially available from Gentex Optics, Inc.) were surfacetreated by washing with soap and water, rinsing with deionized water andisopropyl alcohol, and air drying. The lenses were then plasma treated.For example, 10A no additional coating was applied to the lens. Forexample 10B, the plasma-surface treated lens was coated with MSH-200hydrolyzed organosilicate (1% solids) commercially available fromMitsubishi Chemical Corporation, Tokyo, Japan. For Example 10C, theplasma-surface treated lens was coated with a composition of the typedescribed in Example 6, composition E by dip coating at an extractionrate of 230 mm/min.

Fogging property was evaluated by placing the lens over a cup filledwith hot water. The lens of Example 10A fogged over the entire areathereof. The lens of Example 10B fogged over 50-60% of the area thereof.The lens of Example 10C has not fogging on the surface thereof.

Example 11 Resistance to Fouling by Automotive Break Dust

This Example is intended to illustrate the anti-fouling properties ofthe present invention. Two aluminum alloy wheels purchased fromDaimlerChrysler were divided into five even areas using masking tape.The wheels were installed on a 1996 model Chrysler Jeep Cherokee withone wheel (wheel #1) being installed on the front passenger side, andthe other wheel (wheel #2) being installed on the front driver's side.Prior to installation, the five areas of each of wheel #1 and wheel #2were treated as follows.

Wheel #1 Preparation

Prior to installation on the vehicle, the five areas of wheel #1 weretreated as follows. No coating was applied to Area 1. Area 2 was coatedwith Hi-Gard™ 1080 (an organosilane-containing coating solutionavailable from PPG Industries, Inc.) by curtain coating using a washbottle, air drying for 5 minutes, and the baking at 240° F. (116° C.)for 3 hours. Area 3 was coated with Hi-Gard 1080 as described above forArea #2. After baking, Area,3 was then coated with MSH-200 hydrolyzedorganosilicate (1% solids) commercially available from MitsubishiChemical Corporation, Tokyo, Japan by wipe on application with a soakedsponge. The MSH-200 was then allowed to air dry and self-condense. Area4 was coated with Hi-Gard 1080 as described above for Area 2. Afterbaking, Area 4 was coated with a composition of the type described inExample 6, composition E and a mixture of deionized water: and ethanol(50/50 weight ratio) by wipe-on application using a soaked sponge. Area5 was coated with a composition of the type described in Example 6,composition E.

The vehicle was driven for one Week. Areas 1 through 5 of Wheel #1showed no significant difference in cleanliness prior to a water rinse.After being rinsed with water from a garden hose, the cleanliness ofAreas 1 to 5 of wheel #1 was measured on a scale of 1 to 10 with highernumber reflecting a cleaner surface. The results are summarized in Table8. TABLE 8 Area Cleanliness 1 2 2 6 3 8 4 10 5 10

Wheel #2 Preparation

Prior to installation on the vehicle, the five areas of wheel #2 weretreated as follows. No coating was, applied to Area 1. Area 2 was coatedwith SolGard® 330 coating (an organosilane-containing coating solutionavailable from PPG Industries, Inc.) by curtain coating using a washbottle, air drying for 5 minutes, and the baking at 240° F. (116° C.)for 3 hours. Area 3 was coated with Hi-Gard 1080 as described above forArea.2. After baking, Area 3 was then coated with MSH-200 hydrolyzedorganosilicate (1% solids) commercially available from MitsubishiChemical Corporation, Tokyo, Japan by wipe on application with a soakedsponge. The MSH-200 was then allowed to air dry and self-condense. Area4 was coated with Hi-Gard 1080 as described above for Area 2. Afterbaking, Area 4 was coated with a composition of the type described inExample 6, composition E and a mixture of deionized water and ethanol(50/50 weight ratio) by wipe-on application using a soaked sponge. Area5 was coated with a composition of the type described in Example 6,composition E.

The vehicle was driven for one week. Areas 1 through 5 of wheel #1showed no significant difference in cleanliness prior to a Water rinse.After being rinsed with water from a garden hose, the cleanliness ofAreas 1 to 5 of wheel #1 was measured on a scale of 1 to 1 0 with highernumber reflecting a cleaner surface. The results are summarized in Table9. TABLE 9 Area Cleanliness 1 2 2 8 3 10 4 10 5 10

It will be readily appreciated by those skilled in the art thatmodifications may be made to the invention without departing from theconcepts disclosed in the foregoing description. Such modifications areto be considered as included within the following claims unless theclaims, by their language, expressly state otherwise. Accordingly, theembodiments described in detail herein are illustrative only and are notlimiting to the scope of the invention, which is to be given the fullbreadth of the appended claims and any and all equivalents thereof.

1. A multi-layer coating comprising: (1) a,first layer comprising aninorganic oxide network, and (2) a second layer applied over at least aportion of the first layer, wherein the second layer is deposited fromat least one liquid composition that is hydrophilic and comprises anessentially completely hydrolyzed organosilicate.
 2. The multi-layercoating of claim 1, wherein the first layer is deposited from acomposition comprising a sol containing a network-forming metalalkoxide.
 3. The multi-layer coating of claim 2, wherein thenetwork-forming metal alkoxide comprises an alkoxysilane of the generalformula R_(x)Si(OR′)_(4-x) wherein R is an organic radical, R′ is analkyl radical selected from the group consisting of methyl, ethyl,propyl, and butyl radicals, and x is an integer and less than
 4. 4. Themulti-layer coating of claim 1, wherein the first layer is transparent.5. The multi-layer coating of claim 1, wherein the liquid compositionfrom which the second layer is deposited further comprises aphotocatalytic material.
 6. The multi-layer coating of claim 5, whereinthe average crystalline diameter is 3 to 35 nanometers.
 7. Themulti-layer coating of claim 5, wherein the photocatalytic material isselected from the group consisting of the brookite form of titaniumdioxide, titanium dioxide chemically modified by flame pyrolysis,nitrogen doped titanium dioxide, plasma treated titanium dioxide, andmixtures thereof.
 8. The multi-layer coating of claim 5, wherein thephotocatalytic material is present in the liquid composition in anamount ranging from 0.1 to 0.75 percent by weight based on the totalweight of the composition.
 9. The multi-layer coating of claim 1,wherein the organosilicate of the liquid composition from which the,second layer is deposited is selected from the group consisting oforganoxysilanes, organoxysiloxanes, and mixtures thereof, wherein theorganoxysilanes are selected from the groups consisting oftetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane,tetraisopropoxysilane, tetra-n-butoxysilane, tetraisobutoxysilane,tetra-sec-butoxysilane, tetra-t-butoxysilane, tetraphenoxysilane,dimethoxydiethoxysilane, and mixtures thereof.
 10. The multi-layercoating of claim 1, wherein the organosilicate is present in the liquidcomposition from which the second layer is deposited in an amountranging from 0.1 to 2 percent by weight calculated as SiO₂, based on thetotal weight of the composition.
 11. The multi-layer coating of claim 1,wherein the pH of the liquid composition from which the second layer isdeposited is no more than 3.5.
 12. The multi-layer coating of claim 1,wherein the pH of the liquid composition from which the second layer isdeposited is from 7.0 to 8.5.
 13. A substrate coated with themulti-layer coating of claim
 1. 14. The substrate of claim 13, whereinthe substrate comprises a polymeric substrate.
 15. The substrate ofclaim 14, wherein the polymeric substrate comprises a solid transparentor optically clear solid material.
 16. The substrate of claim 15,wherein the polymeric substrate comprises a photochromic material. 17.The multi-layer coating of claim 1, wherein the second layer is appliedat a dry film thickness of 20 to 60 nanometers.
 18. The multi-layercoating of claim 1, wherein the binder is prepared by a process selectedfrom: (a) a multi-stage process comprising a first stage wherein apartial-hydrolys is polycondensation reaction product is formed byreacting an organosilicate water in the presence of an acid hydrolysiscatalyst, wherein the water is present in an amount that is less thanthe stoichiometric amount capable of hydrolyzing the organoxy groups ofthe organosilicate, and a second stage wherein the partial hydrolysispolycondensation reaction product is contacted with a large amount ofwater to form an essentially completely hydrolyzed organosilicate, and(b) reacting a tetraalkoxysilane oligomer with water in the presence ofan organic acid hydrolysis catalyst and/or an organic solvent, whereinthe water is present in an amount that is considerably greater than thestoichiometric amount capable of hydrolyzing organoxy groups of thealkoxysilane to form an essentially completely hydrolyzedorganosilicate.
 19. The multi-layer coating of claim 18, wherein thebinder is prepared by the multi-stage process.
 20. The multi-layercoating of claim 19, wherein the water is present during the first stagein a stoichiometric amount capable of hydrolyzing 50 percent of theorganoxy groups of the organosilicate.
 21. The multi-layer coating ofclaim 19, wherein the first stage is conducted at conditions that limitthe degree of condensation of Si—OH groups formed as a result of thehydrolysis reaction.
 22. The multi-layer coating of claim 21, whereinthe conditions that limit the degree of condensation of Si—OH groupsformed as a result of the hydrolysis reaction are selected fromcontrolling the reaction exotherm by external cooling, controlling therate of addition of the acid catalyst, and/or conducting the first stagehydrolysis in the substantial absence of any organic cosolvent.
 23. Amethod for improving the anti-fouling, self-cleaning, easy-to-clean,and/or anti-fogging properties of an article, wherein the articlecomprises a surface having, a coating layer comprising an inorganicoxide network deposited thereon, the method comprising the steps of: (1)applying to at least a portion of the surface a liquid compositioncomprising an essentially completely hydrolyzed organosilicate; and (2)curing the composition applied in step (1).
 24. The method of claim 23,wherein step (2) is accomplished by air drying.
 25. The method of claim23, wherein the coating layer comprising an inorganic oxide networkcomprises a network forming metal alkoxide.
 26. The method of claim 25,wherein the network forming metal alkoxide comprises an alkoxysilane ofthe general formula R_(x)Si(OR)_(4-x) wherein R is an organic radical,R′ is an alkyl radical selected from the group consisting of methyl,ethyl, propyl, and butyl, radicals, and x is an integer and less than 4.27. The method of claim 23, wherein the liquid composition applied instep (1) further comprises a photocatalytic material.
 28. The method ofclaim 27, wherein the photocatalytic material comprises a metal oxideselected from the group consisting of zinc oxide, tin oxide, ferricoxide, dibismuth trioxide, tungsten trioxide, strontium titanate,titanium dioxide, and mixtures thereof.
 29. The method of claim 27,wherein at least a portion of the photocatalytic material is present inthe form of particles having an average crystalline diameter of 3 to 35nanometers.
 30. The method of claim 27, wherein the photocatalyticmaterial is selected from the group, consisting of the brookite form oftitanium dioxide, titanium dioxide chemically modified by flamepyrolysis, nitrogen doped titanium dioxide, plasma treated titaniumdioxide, and mixtures thereof.
 31. The method of claim 27, wherein thephotocatalytic material is present in the liquid composition applied instep (1) in an amount ranging from 0.1 to 0.75 percent by weight basedon the total weight of the composition.
 32. The method of claim 23,wherein the organosilicate of the liquid composition applied in step (1)is selected from the group consisting of organoxysilanes,organoxysiloxanes, and mixtures thereof.
 33. The method of claim 23,wherein the organosilicate is present in the liquid composition appliedin step (1) in an amount ranging from 0.1 to 2 percent by weightcalculated as SiO₂, based on the total weight of the composition. 34.The method of claim 23, wherein the pH of the liquid composition appliedin step (1) is no more than 3.5.
 35. The method of claim 23, wherein thesurface comprises a solid transparent or optically clear solid material.36. The method of claim 23, wherein the surface comprises a photochromicmaterial.
 37. The method-of claim 23, wherein the liquid compositionapplied in step (1) is applied at a dry film thickness of 20 to 60nanometers.